Method and device for treating cardiac arrhythmias

ABSTRACT

The present invention provides both methods and devices for termination of arrhythmias, such as ventricular or atrial tachyarrhythmias. The device and method involves application of alternating current (AC) for clinically significant durations at selected therapeutic frequencies through the cardiac tissue to a subject experiencing arrhythmia. Methods are also provided to minimize or eliminate pain during defibrillation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 15/826,498 filed Nov. 29, 2017, now pending; which is a continuationapplication of U.S. application Ser. No. 14/604,457 filed Jan. 23, 2015,now issued as U.S. Pat. No. 10,532,216; which is continuationapplication of U.S. application Ser. No. 14/162,604 filed Jan. 23, 2014,now abandoned; which is a continuation-in-part application of U.S.application Ser. No. 13/393,821 filed Apr. 30, 2012, now abandoned;which is a 35 USC § 371 National Stage application of InternationalApplication No. PCT/US2010/047859 filed Sep. 3, 2010, now expired; whichclaims the benefit under 35 USC § 119(e) to U.S. Ser. No. 61/239,470filed Sep. 3, 2009, now expired. The disclosure of each of the priorapplications is considered part of and is incorporated by reference inthe disclosure of this application.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates generally to medical treatments and morespecifically to a method and device for treating arrhythmias of theheart, such as tachycardia and cardiac fibrillation.

Background Information

Arrhythmia is a variation from the normal rhythm of the heartbeat.Cardiac arrhythmias are an important cause of morbidity and mortality.The major cause of fatalities due to cardiac arrhythmias is the subtypeof ventricular arrhythmias known as ventricular fibrillation (VF).Conduction of electrical impulse is a unique property of cardiac andskeletal muscle and nervous tissue and is fundamental to theirphysiologic function. Abnormal cardiac electrical impulse generation andpropagation underlies the pathogenesis of several diseases, includingventricular fibrillation (see, Santinelli et al., Int J Cardiol.,3(1):109-111 (1983); Kanani et al., J Cardiovasc Pharmacol. 32(1):42-48(1998); and Amitzur et al., Cardiovasc Drugs Ther., 17(3):237-247(2003)), a leading cause of death in the developed world.

To stop VF in an attempt to return the heart to a normal rhythm,automatic external defibrillators (AED) are widely in use in healthcareand non-healthcare settings. In addition, implantable defibrillators arehighly useful in management of a number of chronic heart conditions. Forexample, Sudden Cardiac Death (SCD), which is often due to ventricularfibrillation, accounts for over 400,000 deaths annually in the UnitedStates. Several clinical trials have shown survival benefit in SCDsurvivors who receive implantable defibrillators. Recent trials havealso shown that patients who are at risk for SCD also benefit from thistherapy and implantable defibrillators have been used in this populationwith significant reduction in mortality.

The physical structure of defibrillator systems can be generallyillustrated with reference to the implantable format. Such defibrillatorsystems contain a hermetically sealed “Can” that houses the battery,electronic circuitry and capacitors. These devices are implanted in thechest wall and electrodes are deployed intravascularly to stimulate,pace and deliver high energy defibrillatory shocks to defibrillate theheart. The electrode/lead is typically placed through the subclavianvein into the endocardium.

Three modes of therapies are used by the implantable defibrillators totreat dangerous arrythmias: 1) anti-tachycardia pacing; 2) low energycardioversion; and 3) high energy defibrillation. Among the three, onlyhigh energy defibrillation has been shown to be effective indefibrillating the heart during ventricular fibrillation.

Several different electrode configurations have been used to deliver thehigh energy including, epicardial lead systems (U.S. Pat. Nos. 5,342,407and 5,603,732), endocardial lead systems, and subcutaneous electrodes(U.S. Pat. Nos. 5,133,353, 5,261,400, and 5,620,477). The housing of thedefibrillator can also serve as an additional electrode during deliveryof defibrillatory shocks and for pacing (U.S. Pat. No. 5,658,321).Recently, a totally subcutaneous-non-vascular system that is capable ofdelivering pacing and high voltage defibrillatory shocks has also beendescribed (U.S. Pat. No. 7,536,222).

Currently the principal approach to terminating fibrillation usingimplantable or external systems is by delivering a high voltage DC shockto cause defibrillation of the heart. This is achieved by charging acapacitor and delivering the charge to the heart over a period oftypically 4-16 msec. As such, the current defibrillator circuitryincludes high performance capacitors capable of rapidly charging anddischarging charge, causing a brief period of high current density inthe myocardium that causes defibrillation. There may be multiplecapacitors controlled by a circuit and typically 5-40 Joules of energyare delivered to achieve defibrillation.

While effective in many cases, existing defibrillation systems havedrawbacks. For example, the energy delivered may be insufficient inmagnitude or timing of delivery to stop fibrillation. Low frequency DCand AC are known to be pro-fibrillatory. In addition, the large electricfield applied in defibrillation also leads to significant skeletalmuscle stimulation which has been implicated in the pain that followsdefibrillation shocks.

Further, the current methodology used to treat cardiac arrhythmias usingDC fields is associated with a host of adverse effects that includecellular injury by way of electroporation (see, Tung, Methods Mol Biol.,48:253-271 (1995); Tung et al., Ann N Y Acad Sci., 720:160-175 (1994);and Al-Khadra et al., Circ Res., 87(9):797-804 (2000)), cardiacconduction disturbances (see, Kanani et al., J Cardiovasc Pharmacol.,32(1):42-48 (1998); and Eysmann et al. Circulation., 73(1):73-81(1986)), mechanical dysfunction (see, Tung et al., Ann N Y Acad Sci.,720:160-175 (1994); Mollerus et al., J Interv Card Electrophysiol.,19(3):213-216 (2007); and Tokano et al., J Cardiovasc Electrophysiol.,9(8):791-797 (1998)), and increased mortality due to heart failure (see,Moss et al., N Engl J Med, 346(12):877-883 (2002); and Bardy et al., NEngl J Med., 352(3):225-237 (2005)).

The present invention is based on the discovery of the previouslyunrecognized biophysical phenomenon of reversible cardiac conductionblock using sustained AC fields that is without residualelectrophysiological consequence and can be applied with less perceivedpain than existing defibrillatory methods. Cardiac cells remain in arefractory state for the duration of field stimulation by elevation ofV_(m), a phenomenon that is distinctly different from the effect of DCfields. Further, the cell response to sustained AC fields appears to bedevoid of the deleterious effects commonly observed during DC fieldstimulation. Hence, cardiac conduction block using AC may provide asafer alternative for terminating cardiac arrhythmias.

Low frequency AC (50-60 Hz) waveforms were the first form of electricaltherapy used to treat VF, but was abandoned because of its high risk ofproarrhythmia (see, Gurvich et al., Am Rev Sov Med., 4(3):252-256(1947); Smith et al., Am J Pathol., 47:1-17 (1965); and Lown et al. Am JCardiol., 10:223-233 (1962). Indeed, 50 Hz AC has successfully found itsway into the current generation implantable defibrillators as anefficient way to induce VF (see, Malkin et al., Med Biol Eng Comput.,41(6):640-645 (2003); and Mower et al. Circulation., 67(1):69-72(1983)).

However, few studies have evaluated the effects of higher AC frequenciesin intact hearts. Previous studies used AC in intact guinea pig heartsand demonstrated a frequency-dependent increase in pacing threshold(see, Weirich et al. Basic Res Cardiol., 78(6):604-616 (1983)) andfibrillation threshold (see, Weirich et al. Basic Res Cardiol.,78(6):604-616 (1983); and Geddes et al., Med Biol Eng., 7(3):289-296(1969)) for frequencies up to the kilohertz range.

Roberts et al. evaluated the defibrillation efficacy of AC frequenciesup to 1 kHz, but with a maximum duration of 32 cycles (Pacing ClinElectrophysiol., 26(2 Pt 1):599-604 (2003). They concluded that a 200Hz, 2 cycle waveform was most effective to achieve externaldefibrillation.

Sweeney et al. used monophasic rectangular pulses for open chestdefibrillation in dogs and showed that the energy and currentrequirement was significantly higher at frequencies >1 kHz (J CardiovascElectrophysiol., 7(2):134-143 (1996).

All the above studies relied on defibrillation by the onset of theelectric field, and none of the studies explored longer duration fieldpulses to block conduction as a way to prevent re-initiation of VF.Although conduction block might be expected in the range of frequenciestested in these previous studies, this biophysical phenomenon was notspecifically explored. More importantly, the short duration of the highfrequency AC field (2-32 cycles) might not have been sufficient toextinguish multiple reentrant wave fronts present in VF.

However, the cellular electrophysiological effects of sinusoidal ACfield stimulation have not been systematically studied in cardiactissue. Meunier et al. demonstrated prolongation of action potentialduration in cardiac tissue subject to low frequency (50 Hz) sinusoidalAC stimulation (J Cardiovasc Electrophysiol., 12(10):1176-1184 (2001);and J Cardiovasc Electrophysiol., 10(12):1619-1630 (1999)). The plateauof the action potential remained elevated, and the amplitude of V_(m)oscillation was inversely related to the frequency of AC field up to 100Hz, the maximum frequency used in their study.

Frequency dependent conduction block in excitable tissue such as theneural axons and peripheral nerves have been demonstrated (see, Tanner,Nature, 195:712-713 (1962); and Woo et al., Bulletin Los AngelesNeurological Society, 29:87-94 (1964)). Kilgore et al. reported highfrequency nerve conduction block in the peripheral nerve using 3-5 kHzbiphasic current (Kilgore et al., Med. Biol. Eng. Comput., 42:394-406(2004)). Animal experiments have also shown that high-frequencyalternating electrical current applied to peripheral nerves can blockconduction of action potentials (see, Tanner, Nature, 195:712-713(1962); Reboul et al., Am. J. Physiol., 125:205-215 (1939); Rosenbluethet al., Am. J. Physiol., 125:251-264 (1939); and Bowman et al., Appl.Neurophysiol., 49:121-138 (1986)). This nerve block was quicklyreversible once the stimulation was removed suggesting that this was notdue to repeated stimulation resulting in fatigue (see, Kilgore et al.,Med. Biol. Eng. Comput., 42:394-406 (2004)). Subsequently, others havereported similar findings in a lumped circuit model of the myelinatedaxon based on Frankenhaeuser-Huxley model. The mode of conduction blockwas demonstrated to be due to constant activation of potassium channels,thus antagonizing sodium channel induced depolarization (see, Zhang etal., IEEE Trans. Biomed. Eng., 53:2445-54 (2006)). To date, however,such methods are not being applied to the heart; e.g., to minimize painassociated with the delivery of a defibrillating current.

Further, use of radio frequency (RF) energy has been used to producetemporary conduction block in local areas of a heart. U.S. Pat. No.6,431,173 describes a method of using electrical energy to producetemporary conduction block in a local region of the patient's myocardiumto disrupt a reentry pathway through which an atrial or ventriculartachycardia (or other type of arrhythmia) is initiated and perpetuated,thereby resulting in cardioversion or defibrillation. However, use of RFto for terminating tachyarrhythmias may cause permanent myocardialdamage.

Based on the current state of treatment of arrhythmias, there is a needfor an improved device and method to terminate cardiac fibrillation toprovide less painful treatment of arrhythmias.

SUMMARY OF THE INVENTION

The present invention provides both a method and device for terminationof arrhythmias, such as ventricular or atrial tachyarrhythmias. Thedevice and method involves application of alternating current (AC) forclinically significant duration within a selected range of therapeuticfrequencies applied through the cardiac tissue of a subject experiencingarrhythmia.

In one aspect, a method of treating cardiac arrhythmia in a subject inneed thereof is provided. The method comprises administering a highfrequency AC to a cardiac tissue of the subject, thereby treating thecardiac arrhythmia. In various embodiments, the AC is administered at afrequency between about 50 Hz to 20 KHz. In various embodiments, the ACis administered for a duration between about 0.025 to 2 seconds. Inexemplary embodiments, the AC is administered for at least 0.050 or0.100 seconds.

In another aspect of the invention, the method includes a tiered therapyto alleviate or treat cardiac arrhythmia. The method may includeadministration of AC in a staged progression of multiple tiers. Forexample, tiered therapy may include applying AC along a progression ofdifferent frequencies and durations, the progression continuing untilthe arrhythmia is terminated. As such, the method may include applying aseries of different frequencies of AC, or AC in combination with DC,until the arrhythmia is terminated.

In another aspect of the invention, the method includes a combinedapproach to therapy to alleviate or treat cardiac arrhythmia as well asreducing pain. The method may include applying AC at different distinctfrequencies to achieve neuromuscular blocking effects in addition toarrhythmia termination. In one embodiment, a first frequency of betweenabout 1 kHz to 20 kHz is applied to achieve neuromuscular blockingeffects, such a reduction in pain stimulus. In a related embodiment, asecond frequency of between about 100 Hz to 1 kHz is applied to achievearrhythmia termination. The frequencies may be applied simultaneously orthe first frequency may be applied before the second to effectivelyblock any pain associated with delivery of the second frequency.

In another aspect of the invention, the method includes a combinedapproach to therapy to alleviate or treat cardiac arrhythmia as well asreducing pain. The method may include applying AC at one or morefrequencies in combination with an electric shock, such as a monophasicor biphasic shock. In one embodiment, application of the AC beginsbefore application of the electric shock. In another embodiment, theelectric shock is applied before application of the AC begins. In yetanother embodiment, the electrical shock is monophasic, and the shockincludes an onset prior to onset of the AC and the shock terminatesafter onset of the AC.

In various aspects and embodiments, the method includes detecting theoccurrence of arrhythmia before, after or during the AC is administered.

In another aspect of the invention, a method for treatingtachyarrhythmia in a subject is provided for emergency life support of asubject having cardiac tissue that is in an intractably fibrillatedstate. The method includes administering a plurality of high frequencyalternating current (AC) pulses to a cardiac tissue of the subject,wherein the cardiac tissue is in an intractably fibrillated statebetween administration of each AC pulse, thereby treating thetachyarrhythmia. In one embodiment, each AC pulse has a duration ofabout 0.1 to 2 seconds. Pulsed AC application in this instance allowsthe cardiac muscle to fibrillate between AC pulses to achieve electricalactivation of the ventricles and generation of a mechanical systole.

In another aspect, a device for treating arrhythmia is provided. Thedevice includes a computer-readable program containing one or morealgorithms for generating and/or delivering AC and/or electrical shock,a plurality of electrodes, a waveform generator generating highfrequency AC and/or electrical shock, and optionally, a sensing circuitallowing detection of arrhythmia in a subject and automaticadministration of AC. In one embodiment, the device is configured togenerate AC having a frequency between about 50 Hz to 20 kHz in responseto operation of the computer-readable program.

In another aspect of the invention, the device is configured to delivertiered therapy to a subject to alleviate or treat cardiac arrhythmia. Assuch, in one embodiment, the device is configured to generate and applyone or more different frequencies of AC.

In another aspect of the invention, the device is configured toadminister emergency assistance to a subject experiencing intractablecardiac fibrillation.

In various aspects and embodiments, the device of the present inventionmay be configured such that the plurality of electrodes are disposedintravascularly or intracardiacly, extravascularly or externally, orboth. The device may be fully or partially implantable, or be configuredwholly external to the subject.

In another aspect, a method of generating local conduction block ofcardiac tissue is provided. The method includes administeringalternating current (AC) to a targeted site of a heart during anarrhythmia to cause termination of the arrhythmia. In one embodiment,the AC is administered at a frequency between about 100 Hz to 1 kHz. Ina related embodiment, the AC is delivered via a catheter including aplurality of electrodes. In various embodiments, delivery of the AC istimed to a surface electrocardiogram or an intracardiacelectrocardiogram.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a graphical representation of one embodiment of the deviceof the present invention, wherein the device is configured as anautomatic internal defibrillator (AID).

FIG. 2 shows a graphical representation of one embodiment of the deviceof the present invention wherein the device is configured as anautomatic external defibrillator (AED).

FIGS. 3A, 3B and 3C show graphical representations of the effects of ACelectric field stimulation on propagation of paced impulses acrossconfluent monolayers (n=15) of neonatal rat ventricular cardiomyocytes.FIG. 3A is a graphical representation of the effects of application of a1 kHz AC field. FIG. 3B is a graphical representation of the effects ofapplication of a 100 kHz AC field. FIG. 3C is a graphical representationof the effects of application of a 10 kHz AC field. In FIGS. 3A-3C, thetop panels of each show voltage maps before, during, and after AC field.For each, the monolayer was paced from the left edge by a bipolar pointelectrode at 6 Hz (for A) or 3 Hz (for B and C). In FIGS. 3A-3C, thebottom panels in each case show a representative voltage trace from thecenter of the monolayer at site x. Vertical lines along the x-axisdenote the time of point stimuli, while the gray bar denotes the time ACfield is on. As shown, AC field stimulation is effective in producingpropagation block when applied at some frequencies (e.g., 1000 Hz inFIG. 3A), but not at others (e.g., 100 Hz in FIG. 3B or 10 kHz in FIG.3C).

FIGS. 4A, 4B and 4C show graphical representations of AC electric fieldpulse terminating pinned spiral wave reentry. FIG. 4A shows a series ofvoltage maps before, during, and after a 1 kHz 1-sec duration AC pulse.Numbers above maps denote time in msec. Maps with gray backgroundindicate that the AC pulse is on. FIG. 4B shows a representative voltagetrace from site a of FIG. 4A (top left) showing stable train of actionpotentials before the AC pulse, and sustained partial depolarizationduring AC delivery, with prompt return to resting potential when ACstimulation is turned off. FIG. 4C shows voltage traces at sites a-f ofFIG. 4A (top row) at an expanded time scale at the time of AC fieldonset. In FIGS. 4B and 4C, the gray bar denotes the time the AC pulsewas on.

FIGS. 5A and 5B show graphical representations summarizing data of DCand AC field pulse effects on conduction (n=15 monolayers) and reentry(n=11). Not all field strengths and frequencies were tested in eachmonolayer. FIG. 5A shows a plot summarizing conduction experiments. Inconduction experiments, the response during the pulse was characterizedas no effect, field-evoked activity (FEA), or block, as described inFIGS. 3A-3C. Post-pulse ectopic activity (PPEA), as shown in FIGS.3A-3C, was also identified separately. FIG. 5B shows a plot summarizingreentry experiments. In reentry experiments, the response wascharacterized as no effect, FEA+termination, termination, orre-initiation, as described in Examples. Note similarity in theparameter spaces for conduction and reentry, with regions of block inFIG. 5A corresponding to termination in FIG. 5B (X for each), FEA inFIGS. 5A and 5B (triangles), and no effect (circles).

FIGS. 6A and 6B show graphical representations of simulations of ACfield pulses. In both FIGS. 6A and 6B, the top panels show voltage mapsbefore, during, and after a 500 Hz, 300-arbitrary units (a.u.) fieldstrength, 1-sec duration AC pulse. Time (in msec) is denoted above themaps. Maps with gray background denote times during which the AC pulseis on. In both FIGS. 6A and 6B, the bottom panels show the transmembranevoltage (V_(m)), sodium current (I_(Na)), and intracellular calcium([Ca]_(i)) at a site denoted by the pink dot on the first voltage map.The gray bar denotes the time the AC field pulse is on. FIG. 6A showsapplication of 500 Hz AC field. Vertical lines along the lower x-axisdenote the times of point stimuli. FIG. 6B shows application of a 500 HzAC field.

FIGS. 7A and 7B show graphical representations of defibrillation of awhole heart by a 1 second duration pulse of AC.

FIGS. 8A and 8B show graphical representations of successfuldefibrillation of a whole heart by a 50 ms pulse (FIG. 8A) and faileddefibrillation by a 30 ms pulse (FIG. 8B).

FIGS. 9A, 9B and 9C show graphical representations of administration ofa ramped high frequency AC waveform plus biphasic shock and subsequentresponse thereto. FIG. 9A shows an illustrative ascending high frequencyAC ramp followed immediately by biphasic shock. FIG. 9B shows skeletalmuscle force response (black) to ramped high frequency AC stimulationthat precedes 400 V biphasic shock (grey). FIG. 9C shows muscle forceresponse (black) to 400 V biphasic shock alone (grey).

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides methods for using selected therapeuticfrequencies of AC to cause termination of arrhythmia. The mechanisms bywhich the AC terminates arrhythmia are based on the generation ofpositively- and negatively-polarized areas in the heart by the appliedfield, separately by a voltage gradient. The sequential reversal of thepolarity of these regions of membrane polarization by the applied AC,combined with the non-linear response of the membrane to theshock-induced polarization, results in a sequential decrease in thevoltage gradient between the regions of opposite polarity until thisgradient reaches a value that is insufficient for the generation of anew wavefront at the border between regions of opposite membranepolarity. The frequency range minimizes proarrythmia, which has been themajor drawback of low frequency electrical current. The inventionprovides additional embodiments wherein the high frequency AC isprovided in combination with AC at other frequencies or DC in a tieredtherapy to terminate arrhythmia and/or co-terminously to block pain.

Thus, the present invention provides an alternative mechanism to use ofDC fields to achieve termination of cardiac arrhythmias by causingconduction block using sustained AC field. It is expected that ACfield-induced, reversible conduction block will have widespreadapplicability in both external and implantable medical devices to treatarrhythmias. Finally, based the observations discussed herein using ACin cardiac tissue, in conjunction with reports on nerve block using highfrequency AC, it can be expected that AC stimulation could be utilizedto block both cardiac and nerve conduction during arrhythmias to achievepainless defibrillation.

Before the present devices and methods are described, it is to beunderstood that this invention is not limited to particular devices,methods, and experimental conditions described, as such devices,methods, and conditions may vary. It is also to be understood that theterminology used herein is for purposes of describing particularembodiments only, and is not intended to be limiting, since the scope ofthe present invention will be limited only in the appended claims.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural references unless the contextclearly dictates otherwise. Thus, for example, references to “themethod” includes one or more methods, and/or steps of the type describedherein which will become apparent to those persons skilled in the artupon reading this disclosure.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the invention, the preferred methods andmaterials are now described.

The present invention is based in part on the discovery of a novelbiophysical phenomenon of reversible block of cardiac conduction duringsustained sinusoidal alternating current (AC) field stimulation. Whilenot wishing to be bound by any theory as to mechanism of action, it isbelieved that, when applied according to the invention, an appropriate(not pro-fibrillatory) AC field paralyzes affected cardiac cells bymaintaining them in a partially depolarized state and rendering themrefractory to pacing stimuli. This effect is completely reversible oncessation of the AC field (see, e.g., Example 1 and FIGS. 3-7). AC fieldterminated reentrant spiral waves by depolarizing the entire excitablegap and maintaining an elevated transmembrane potential (V_(m))throughout the monolayer, thus preventing re-initiation of reentry.Computer simulations of sustained AC field in a three-dimensionalbidomain model of guinea pig ventricular myocardium reproduced theconduction block and revealed inactivation of Na channels for theduration of the field. Cardiac conduction was unaffected during directcurrent field, suggesting that conduction block was unique to sustainedAC stimulation.

As such, the present invention is based on the seminal discovery of areversible conduction block in cardiac tissue using sustained AC fieldthat provides a novel method to terminate cardiac arrhythmias.Reversible conduction block by AC has broad applicability in clinicalcardiac electrophysiology.

The present invention provides both a method and device for terminationof arrhythmias, such as ventricular or atrial tachyarrhythmias. Thedevice and method involves application of high frequency alternatingcurrent or electric field through the cardiac tissue to a subjectexperiencing arrhythmia, such as tachyarrhythmia.

In one aspect, a method of treating cardiac arrhythmia in a subject inneed thereof is provided. The method comprises administering a highfrequency alternating current (AC) to a cardiac tissue of the subject,thereby treating the cardiac arrhythmia.

In another aspect of the invention, the method includes a combinedapproach to therapy to alleviate or treat cardiac arrhythmia as well asreducing pain. The method may include applying AC at different distinctfrequencies to achieve neuromuscular effects in addition to arrhythmiatermination. In one embodiment, a first frequency of between about 1 kHzto 20 kHz is applied to achieve neuromuscular effects, such a reductionin pain stimulus. In a related embodiment, a second frequency of betweenabout 100 Hz to 1 kHz is applied to achieve arrhythmia termination. Thefrequencies may be applied simultaneously or the first frequency may beapplied before the second to effectively block any pain associated withdelivery of the second frequency.

In another aspect of the invention, the method includes a combinedapproach to therapy to alleviate or treat cardiac arrhythmia as well asreducing pain. The method may include applying AC at one or morefrequencies in combination with an electric shock, such as a monophasicor biphasic shock. In one embodiment, application of the AC beginsbefore application of the electric shock. In another embodiment, theelectric shock is applied before application of the AC begins. In yetanother embodiment, the electrical shock is monophasic, and the shockincludes an onset prior to onset of the AC and the shock terminatesafter onset of the AC.

In various aspects and embodiments, the method includes detecting theoccurrence of arrhythmia before, after or during the AC is administered.

In another aspect of the invention, a method for treatingtachyarrhythmia in a subject is provided for emergency life support of asubject having cardiac tissue that is in an intractably fibrillatedstate. The method includes administering a plurality of high frequencyalternating current (AC) pulses to a cardiac tissue of the subject,wherein the cardiac tissue is in an intractably fibrillated statebetween administration of each AC pulse, thereby treating thetachyarrhythmia. In one embodiment, each AC pulse has a duration ofabout 0.1 to 2 seconds. Pulsed AC application in this instance allowsthe cardiac muscle to fibrillate between AC pulses to achieve electricalactivation of the ventricles and generation of a mechanical systole.

In another aspect, a method of generating local conduction block ofcardiac tissue is provided. The method includes administeringalternating current (AC) to a targeted site of a heart during anarrhythmia to cause termination of the arrhythmia. In one embodiment,the AC is administered at a frequency between about 100 Hz to 1 kHz. Invarious embodiments, delivery of the AC is timed to a surfaceelectrocardiogram or an intracardiac electrocardiogram. In oneembodiment the method of local conduction block is used duringdiagnostic or therapeutic electrophysiologic procedures, where thearrhythmia is electrically mapped and a region critical to thearrhythmia is identified using a catheter based approach. To decidewhether to ablate the region, before application of therapeutic energy(RF or Cryo), alternating current is applied locally to cause conductionblock. If this terminates the arrhythmia then this information will beuseful both for diagnostic and therapeutic purposes.

Ablation may be performed as described in U.S. Pat. No. 6,431,173. Thereare two types of ablative therapy, namely, surgical and catheterablative therapy. The aim of either type of ablative therapy is topermanently destroy (irreversibly damage) the myocardium whichconstitutes the critical part of the reentrant circuit of theventricular or a trial tachycardia which is required to sustain orperpetuate the ventricular or a trial tachycardia. In other words, theablation of the critical region of the myocardium acts to permanentlyeliminate the conduction or impulse formation through the reentrantpathway which is required to sustain or perpetuate the ventricular or atrial tachycardia. Successful ablation is critically dependent on theability to localize the involved myocardium necessary to initiate andperpetuate the ventricular or a trial tachycardia. Diagnostic techniquesused to localize the reentry circuit include analysis of a 12-lead ECG,catheter mapping during a trial or ventricular tachycardia, and pacemapping. Once the site of origin of ventricular or a trial tachycardiais localized, ablative procedures (surgical or catheter directed) can beperformed.

In the catheter ablation approach, catheter-based electrodes are used topermanently disable myocardium tissue adjacent to the electrode withoutaffecting more distant tissue.

Using RF energy (500-1000 kHz, 15-50 W, 100-800 J, 30-75 V rms and 0.1-1A rms, for 10-60 sec.), tissue extending several mm from the electrodeis heated to 65-100° C. This produces permanent lesions that blockreentry or disable the AV node. Particularly in the case of atrialfibrillation, specific anatomical structures are often associated withreentry pathways required to sustain arrhythmias. As a result, theincidence of arrhythmias may decrease and/or the arrhythmias may bebetter organized, thereby leading to a higher degree of success with lowenergy shock therapies. One example of a critical isthmus of conductionfor atrial flutter cited by Lesh and co-workers, is found in the lowerright atrium extending from the inferior vena cava to the coronary sinusostium bordered by the eustachian ridge (ER) and the tricuspid annulus(TA). Lesh et al. also speculate that any lesion connecting theER/crista terminals and the TA could interrupt the atrial flutterreentrant circuit. Although the reentrant pathways for AF are morecomplex and possibly shorter and more numerous, some success has beenachieved with the use of multiple lesions to cure AF.

As used herein, the term “subject” is intended to refer to anyindividual or patient to which the method described herein is performed.Generally the subject is human, although as will be appreciated by thosein the art, the subject may be an animal. Thus other animals, includingmammals such as rodents (including mice, rats, hamsters and guineapigs), cats, dogs, rabbits, farm animals including cows, horses, goats,sheep, pigs, etc., and primates (including monkeys, chimpanzees,orangutans and gorillas) are included within the definition of subject.

As used herein, the term “administration” or “administering” areintended to include an act of applying or delivering alternating currentto cardiac tissue or cells. Typically administration is performed viaexternally disposed or implanted electrodes as described herein.

In another aspect, a device for treating arrhythmia is provided. Thedevice includes a computer or microprocessor-readable program containingone or more algorithms for generating and/or delivering AC and/orelectrical shock, a plurality of electrodes, a waveform generatorgenerating high frequency AC and/or electrical shock, and optionally, asensing circuit allowing detection of arrhythmia in a subject andautomatic administration of AC.

As used herein, high frequency (HF) alternating current (AC) is intendedto include frequencies of between about 50 Hz and 20 kHz. In variousaspects and embodiments, for termination of arrhythmia and painmanagement, the device and method utilize frequencies of between about50 Hz and 1 kHz, 50 Hz and 900 Hz, 50 Hz and 800 Hz, 50 Hz and 700 Hz,50 Hz and 600 Hz, 50 Hz and 500 Hz, 100 Hz and 500 Hz, 100 Hz and 400Hz, 100 Hz and 300 Hz, 100 Hz and 200 Hz, 150 Hz and 500 Hz, 150 Hz and400 Hz, 150 Hz and 300 Hz, 150 Hz and 200 Hz, 500 Hz to 1 kHz and 250 Hzto 500 Hz. Frequencies above 1 kHz are anticipated to be ineffective.Further, it is anticipated that most effective results will be obtained,depending to a degree on duration, within frequency ranges of 150 Hz and300 Hz, including at 200 Hz.

As will be appreciated by those in the art, in various aspects andembodiments of the invention, alternating current may be delivered inany number of waveforms or combinations or waveforms. In variousembodiments, the waveform may be a sinusoidal, triangular, orsquare-wave, as well as any combinations thereof. Additionally,square-waves, may have a duty-cycle of about 25%, 30%, 35%, 40%, 45%,50%, 55%, 60%, 65%, 70%, or 75%. Further, the waveform may switch on oroff abruptly, or may be shaped by an envelope waveform to effect moregradual onset or offset.

In practicing the invention, alternating current may be applied oradministered for various durations of time ranging from about 0.025second to 2 seconds to accomplish termination of the arrhythmia. Invarious embodiments, alternating current may be applied or administeredfor about 0.025 second to 1.5 seconds, or 0.025 second to 1 second,0.025 to 0.5 second. For example, alternating current may be applied oradministered for about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1,1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0 seconds.

As will also be appreciated by those in the art, in various aspects andembodiments of the invention, alternating current may be delivered in aramped waveform, e.g., a waveform having increasing amplitude over time.Such waveforms are useful for blocking or decreasing sensitivity of themuscle to a subsequent delivery of an electrical shock, e.g., amonophasic shock, a biphasic shock, or a combination thereof. Highfrequency AC administered via a ramped waveform blunts the amplitude andthe rate of force developed in skeletal muscle, which results insubstantial mitigation of defibrillation-induced pain.

A ramped waveform of the present invention employs an extended, gradualrise, instead of rising rapidly to its maximum level. The rise time ofthe ramped waveform should be a substantial portion of the duration ofthe waveform and, preferably, at least about 50%, 60%, 70%, 80%, 90%,95% or greater, of the total duration of the waveform. The rampedwaveform may be applied or administered for various durations of timeranging from about 0.025 second to 2 seconds to accomplish terminationof the arrhythmia. In some embodiments, ramped alternating current maybe applied or administered for about 0.025 second to 1.5 seconds, or0.025 second to 1 second, 0.025 to 0.5 second. For example, rampedalternating current may be applied or administered for about 0.1, 0.2,0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7,1.8, 1.9, or 2.0 seconds or greater. Generally, the maximum reduction inmuscle stimulation occurs with a fully ramped waveform, for example, 1second total duration and approximately a 1 second rise time. Afterreaching the maximum current level, the output pulse may continue atthis current level for a short period of time, and then rapidly returnsto 0 over a short fall time. The time period during which the pulse isat its maximum current level may be, for example, 0-0.1 seconds. Assuch, the ramped waveform may begin with an increased amplitude thatcontinues to increase, level off, or otherwise change.

In various embodiments, a high frequency waveform may be continuouslyramped in amplitude during the total duration of application. Theamplitude may be ramped from about 0 to 25, 50, 75, 100, 125, 150, 175,200, 225, 250, 300, 350, 400 or 500 volts or greater.

In various embodiments, the present invention contemplatesadministration of a ramped waveform in combination with an electrical,for instance, a monophasic or biphasic shock. The electrical shock mayfollow the ramped waveform. In one embodiment, the shock waveform thatis administered to the high frequency AC ramp is a decaying exponentialwith time constant 1-10 ms. The peak rising edge voltage of the shockmay be less than, equal to, or greater than the peak of the highfrequency AC ramp. In embodiments, the peak rising edge voltage of theshock is greater than the peak of the high frequency AC ramp, such as10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 120%, 140%, 160%,180%, 200% or greater than the peak of the high frequency AC ramp. Wherethe shock is monophasic, the shock duration may be 4-16 ms. Where theshock is biphasic, the first phase may be 2-6 ms and the second phasemay be 2-12 ms. The shock is preferably applied at the peak or end ofthe HFAC ramp.

As will be appreciated by one skilled in the art, in various aspects andembodiments of the invention, the device may be configured to applyalternating current manually at the discretion of a health care worker,either by an internally implanted or externally applied device, or maybe applied automatically in response to a detected arrhythmia, either byan implanted or externally disposed device. Such applications maycoincide with detection of arrhythmia in the subject by a sensingcircuit allowing detection of the arrhythmia, which may be included inor external to the device.

The device and methodology may be used to treat a number of differenttypes of arrhythmias. Typically, the arrhythmia is a tachyarrhythmia,such as ventricular tachyarrhythmia, or atrial tachyarrhythmia.Ventricular tachyarrhythmias may include, but are not limited toventricular fibrillation. Atrial tachyarrhythmias may include, but arenot limited to atrial fibrillation and atrial flutter.

The device and methodology utilize a plurality of electrodes which maybe configured in a variety of ways to administer alternating current.Alternating current may be administered via a number of electrodeconfigurations as described. When used with an externally applieddevice, the alternating current is preferably applied via largeelectrodes placed on the skin across the heart as is typically done withexternal defibrillators. Automatic response to arrhythmia detection canbe implemented using separate skin electrodes to detect the ECG, orusing the same large electrodes through which the alternating current isthen applied.

When used with an implanted device, the alternating current ispreferentially applied via electrodes placed in or about the cardiacchambers, or via electrodes placed in the chest outside the rib cage,for example in the subcutaneous layers including the housing of theimplanted device itself, or using a combination of such electrodes.Automatic response to arrhythmia detection can be accomplished usingelectrodes placed in or about the cardiac chamber or chamberssusceptible to tachyarrhythmia, or using electrodes placed in the chestoutside the ribcage, for example in the subcutaneous layers.

In one configuration, a device may be in electrical communication with asubject's heart by way of one or more leads, suitable for deliveringmulti-chamber stimulation and pacing therapy. Not every configurationhas all of the electrodes to be described below, but a particularconfiguration may include some of these electrodes. Other configurationsof the device may include even more electrodes than discussed herein.For example, alternating current may be applied by other, additionalelectrodes than those described below. Further, the electrodes anddevice may be configured to apply alternating current using a tieredapproach. Additional electrodes for delivering alternating current caninclude combinations or electrodes situated over the epicardium (e.g.,multiple pacing and relatively larger surface area defibrillationelectrodes that may be used for optimizing cardiac resynchronizationtherapy and providing defibrillation).

Regarding the leads and electrodes, in order to sense atrial cardiacsignals and to provide right atrial chamber stimulation therapy, thedevice may be coupled to an implantable right atrial lead, typicallyhaving an atrial tip electrode and an atrial ring electrode, which maybe implanted in the subject's right atrial appendage. The device is alsoknown as and referred to as a pacing device, a pacing apparatus, acardiac rhythm management device, or an implantable cardiac stimulationdevice.

To sense left atrial and ventricular cardiac signals and to provide leftatrial and ventricular pacing therapy, the device may be coupled to a“coronary sinus” lead configured for placement in the “coronary sinusregion” via the coronary sinus opening for positioning a distalelectrode adjacent to the left ventricle or additional electrode(s)adjacent to the left atrium. As used herein, the phrase “coronary sinusregion” refers to the vasculature of the left ventricle, including anyportion of the coronary sinus, great cardiac vein, left marginal vein,left posterior ventricular vein, middle cardiac vein, and/or smallcardiac vein or any other cardiac vein accessible by the coronary sinus.

Accordingly, a coronary sinus lead may be configured to receive atrialand ventricular cardiac signals and to deliver left ventricular pacingtherapy using a left ventricular (LV) tip electrode and a LV ringelectrode. Left atrial pacing therapy may use, for example, first andsecond left atrial (LA) ring electrodes. Administration of alternatingcurrent can also be performed using at least a coronary sinus coilelectrode. Administration of alternating current can also be performedusing a pair of right atrial (RA) ring electrodes.

The device may also be in electrical communication with a subject'sheart by way of an implantable right ventricular lead, typically havinga right ventricular (RV) tip electrode, an RV ring electrode, an RV coilelectrode, and a superior vena cava (SVC) coil electrode (also known asa right atrial (RA) coil electrode).

The components of the device may be contained in a case, which is oftenreferred to as the “can”, “housing”, “encasing”, or “case electrode”,and may be programmably selected to act as the return electrode forunipolar operational modes. The case may further be used as a returnelectrode alone or in combination with one or more additional electrodesfor stimulating purposes. The case may further include a connectorhaving a plurality of terminals for connecting one or more of thefollowing electrodes in various configurations:

a left ventricular tip electrode;a left ventricular ring electrode;a left atrial coil electrode;a left atrial ring electrode(s);a coronary sinus coil electrode;a right ventricular tip electrode;a right ventricular ring electrode;a right ventricular RV coil electrode;right atrial ring electrode(s);a right atrial tip electrode;a right atrial SVC coil electrode;an epicardial electrode; andsubcutaneous electrode(s).

The device and methodology described herein includes tiered therapy,which provides an adaptive and refined therapy for arrhythmias. Thetiered approach divides therapy for arrhythmias into a progression ofmultiple tiers. For example, tiered therapy may include applyingalternating current along a progression of different frequencies anddurations, the progression continuing until the arrhythmia isterminated.

The progression of tiered therapy may proceed from a least invasivefrequency and duration (e.g., vector) to a more invasive vector,stopping the progression whenever the arrhythmia ceases. In someimplementations, the progression of vectors reflects a progression inthe size of electrodes used to deliver alternating current, and/or aprogression in the area or volume of electrically excitable cardiactissue to be stimulated. This exemplary technique of tiering the vectorsmay minimize pain, especially if the patient is responsive to the leastinvasive vector.

As will be appreciated by one skilled in the art, various aspects of themethodology of the present invention may be combined. For example,tiered therapy may also include application of electric shock inaddition to application of AC. For example monophasic or biphasic shockmay be administered after or before AC is applied in a tiered approach.

The following examples are provided to further illustrate theembodiments of the present invention, but are not intended to limit thescope of the invention. While they are typical of those that might beused, other procedures, methodologies, or techniques known to thoseskilled in the art may alternatively be used.

Example 1 Reversible Conduction Block in Cardiac Tissue Using SinusoidalAlternating Current Field Stimulation

The following experimental methods were followed in this example.

Cell culture was performed as follows. Neonatal rat ventricular myocytes(NRVMs) were dissociated from 2-day old Sprague-Dawley rat hearts withthe use of the enzymes, trypsin and collagenase, as previously described(see, Iravanian et al., AJP Heart Circ., 285(1):H4449-56 (2003)). Theresulting cell suspension was plated at high density onto 21 mm diameterplastic coverslips (106 myocytes per coverslip) to form monolayers thatbecame confluent after 3-4 days of culture. Experiments were performedon days 6 to 8 after plating. For reentry experiments, prior to plating,a 4-mm diameter hole was punched in the coverslip.

Electrophysiological recording was performed as follows. Transmembranevoltage was recorded using contact fluorescent imaging as previouslydescribed (see, Entcheva et al., J Cardiovasc Electrophysiol.,11(6):665-76 (2000)). Briefly, maps of transmembrane potential wererecorded by placing the cell monolayer directly on top of a bundle of253 optical fibers 1 mm in diameter, arranged in a tightly packed,17-mm-diameter hexagonal array. The cell monolayers were stained duringthe experiment with 10 μM di-4-ANEPPS, a fluorescent voltage-sensitivedye, and continually superfused with warmed (37° C.) Tyrode's solution(in mmol/L: 135 NaCl, 5.4 KCl, 1.8 CaCl2, 1 MgCl2, 0.33 NaH2PO4, 5HEPES, 5 glucose).

Electric field stimulation was applied across a parallel set of platinumwires 2.5-cm long placed in the bath outside the monolayer preparation.The field intensity was calibrated from the peak voltage across a pairof AgCl test electrodes placed at a 1.4-cm spacing in the chamber.

The following experimental protocol was used to perform conductionexperiments. A bipolar point electrode was placed near the edge of themonolayer and used to pace the monolayer at 2-6 Hz (10 ms monophasicpulse, 1.5× threshold). Each recording was 3 sec long, with point pacingeither on for the entire recording or turned off for the last 500 ms.After 1 sec, a 1-sec duration AC or DC pulse was applied to themonolayer. For reentry experiments, rapid point pacing was used toinduce a stable spiral wave reentry. Stable reentry was consideredsuccessful if the wave pinned to the hole for at least 1 min. Eachrecording was 3 sec, in which a 1-sec duration AC or DC pulse wasapplied to the monolayer 1 sec after the start of the recording.

Signal processing was performed as follows. Over the duration of theoptical recording, the voltage fluorescence baseline decreased due tophotobleaching and heating of the LED excitation light source. Baselinedrift was corrected for by subtraction of a fitted third-orderpolynomial at each recording site. The individual signals were alsotemporally filtered using a 5-point median filter and range normalizedfrom 0 to 1. Voltage maps were created by interpolating the mapped datato a 100 μm×100 μm grid. Recording channels with poor signal were notused for the interpolation.

Data analysis was performed as follows. For conduction experiments,monolayer responses to DC and AC field were categorized as no effect,field-evoked activity (FEA), or conduction block during the field pulse.In no effect cases, paced conduction continued at the same pacing rateduring the field pulse. In FEA cases, rapid activity faster than thepoint pacing rate was elicited. In conduction block cases, no activationoccurred during the field pulse. The occurrence of post-pulse ectopicactivity (PPEA) was separately identified, when multiple spontaneouswaves were initiated at a location distinct from the point pacing site.

For reentry experiments, monolayer responses were characterized as noeffect, FEA+termination, termination, or reinitiation. In no effectcases, the field did not perturb the spiral wave reentry. InFEA+termination cases, FEA was present during the pulse and ceased atfield offset. In termination cases, the reentry terminated at fieldonset, and no activity was present during the pulse. In reinitiationcases, activity during or after the pulse reinitiated a spiral wave.

The following computational methods were followed.

A cell monolayer model was set-up and represented by a 4.4 cm×4.4cm×0.25 mm tissue mesh centered at the bottom of a perfusate-filledchamber. The electrical properties of the tissue were modeled using anisotropic bidomain representation. To mimic the random orientation ofthe myocytes in the monolayer, the intracellular conductivities werevaried randomly (Plank et al., J Cardiovasc Electrophysiol,16(2):205-216 (2005)). Membrane kinetics of the monolayer wererepresented using the Luo-Rudy dynamic guinea pig ventricular model(Faber et al., Biophys J, 78(5):2392-2404 (2000)), with modificationsfor modeling large external field stimulation (Ashihara et al.,Europace, 7(s2), S155-S165)).

A simulation protocol was also used. In conduction block simulations, apoint electrode was used to pace the tissue at 2 Hz before, during, andafter the AC field pulse. In reentry simulations, an 8-mm hole wasintroduced in the center of the monolayer to allow attachment of thespiral wave. A spiral wave was initiated using an S1-S2cross-stimulation protocol. A one second-duration AC field pulse wasthen applied at varying field strengths and frequencies. AC fieldstimulation was delivered from line electrodes located in thesuperfusing bath, as in the experimental setup.

The following results were observed.

AC Electric Field Stimulation During Pacing: The effect of 1 second ACelectric field stimulation on propagation of paced impulses acrossconfluent monolayers (n=15) of neonatal rat ventricular cardiomyocyteswas explored. At the highest field strength tested in our study (22V/cm), AC field frequencies between 50 Hz and 1 kHz consistentlyresulted in a conduction block across the monolayer (FIGS. 3A and 5A).During the AC field stimulus, the cells were held at an elevatedtransmembrane voltage and point pacing-initiated conduction wascompletely blocked. Immediately following cessation of the AC field, thetransmembrane voltage (V_(m)) returned back to the initial restingpotential, and subsequent paced stimuli initiated propagating wavesacross the monolayer with conduction velocity and propagation patternunchanged from those before AC field stimulation. The results wereconsistent across all the monolayers tested.

The degree of conduction block was frequency- and fieldstrength-dependent. At the highest field strength tested (22 V/cm), ACfrequencies less than 50 Hz resulted in repetitive depolarizations ofthe monolayer, which we term field-evoked activity (FEA) (FIGS. 3B and5A), while frequencies above 2 kHz had no effect on the monolayer (FIGS.3C and 5A). FEA was also elicited at lower field strengths (<10 V/cm)for all frequencies below 2 kHz (FIG. 5A).

Termination of Spiral Wave Reentry by Sustained AC field: Next, theability of sustained AC-induced conduction block to terminate stablespiral wave reentry in monolayers (n=11) was evaluated. AC fields of 22V/cm with frequencies between 20 Hz and 1 kHz consistently terminatedspiral wave reentry. The onset of the AC field depolarized the entireexcitable gap and held V_(m) at an elevated level for the fieldduration, completely extinguishing the spiral wave and preventingre-initiation of activity (FIGS. 4 and 5B). Following AC fieldcessation, V_(m) returned to the resting potential, followed byquiescence. Subsequent pacing stimuli were able to elicit normalpropagated waves (not shown).

AC frequencies <50 Hz or >2 kHz often resulted in FEA during the ACfield pulse followed by either termination of spiral wave reentry orre-initiation of new spiral wave reentry at the offset of the pulse(FIG. 5B). AC fields at even higher frequencies (5-10 kHz) had noappreciable effect on spiral wave reentry. As with conduction block, thefield strength threshold for spiral wave termination wasfrequency-dependent (FIG. 5B).

AC Field vs. Direct Current Field: Point-pacing during the DC fieldinitiated new propagating waves, indicating lack of conduction block(FIG. 5A). A second rapid depolarization was observed at the fieldoffset. Following cessation of the DC field, in all cases, the monolayerwas severely damaged, identified by a rapid decline in optical signalintensity and point pacing initiating highly heterogeneous propagation,producing rapid ectopic activity, or failing to elicit any response.High-strength DC field stimulation terminated spiral wave reentry bydepolarization of the entire excitable gap, similarly to that observedduring AC field stimulation (FIG. 5B). However, as during conductionexperiments, during the DC field pulse V_(m) returned near the restingpotential, FEA was frequently initiated, and the monolayer was severelydamaged. Lower-strength (≤15 V/cm) DC field pulses either initiated FEAor elicited no effect at the lowest field strengths tested (FIGS. 5A andB). Computational Modeling of Reentry Termination and Conduction Blockby AC: Computer simulations were used of a three-dimensional bidomainmodel of guinea pig ventricular tissue to dissect the biophysicalmechanisms of conduction block by sustained AC field stimulation.

Consistent with our monolayer experiments, simulations revealedconduction block of paced waves and termination a stable spiral wavereentry (FIG. 6A) during sustained AC field stimulation. Both conductionand reentry simulations revealed that V_(m) oscillates around anelevated average value ranging from −10 to −20 mV during the AC fieldpulse. The functional consequence of the sustained AC field is a“paralytic” effect that prevents sodium channel recovery frominactivation after V_(m) exceeds the sodium channel activation threshold(−58.8 mV). Intracellular calcium is maintained at an elevated levelduring the pulse, returning to resting levels at field offset (FIG. 6B).

The findings discussed herein reveal an important biophysical effect ofsustained AC on cardiac tissue that is distinctly different from DCfield stimulation. DC field causes a make excitation at its onset and abreak excitation at its offset, and V_(m) returns to resting potentialin between, provided sufficient time between field onset and offset. Onapplication of AC, V_(m) is elevated and oscillates around an elevatedvalue ranging from −10 to −20 mV, blocking conduction and preventingre-initiation of activity.

Computational modeling provided insight into the ionic mechanism ofconduction block. V_(m) oscillated in phase with the frequency of ACfield, but average V_(m) during the field application was elevated abovethe sodium channel activation threshold, indicating that the conductionblock is due in part to the sustained inactivation of cardiac sodiumchannels. The simulation parameter space of the guinea pig model closelymatched the experimental parameter space of neonatal rat cells,demonstrating that these mechanisms are not species-dependent.

Example 2 AC Applied to Whole Hearts

This example presents data showing termination of fibrillation in wholeguinea pig hearts in vivo upon application of AC.

Guinea pigs were perfused as Langendorff preparations. Hearts werestained with the voltage-sensitive dye di-4-ANEPPS (10 μmol/L) by directcoronary perfusion for 10 minutes. An EC uncoupler (diacetyl monoxime)was used to arrest mechanical deformation and the hearts were placed ina custom-built chamber that was attached to a micromanipulator. Opticalaction potential mapping was performed from 128 sites of the intactguinea pig heart. Total mapping field was 1 cm xl cm with an estimateddepth of field of 0.2 mm. The ventricular epicardial surface wasstimulated using bipolar electrodes to induce ventricular fibrillation.Two field electrodes placed on either side of the heart delivered the ACelectric field.

Pulses of AC administered to whole guinea pig hearts was performed. Asshown in FIGS. 7A-7B, defibrillation of a whole heart is evidenced by a1 second pulse of AC. As shown in FIGS. 8A-8B, successful defibrillationof a whole heart by a 50 ms pulse (FIG. 8A) and failed defibrillation bya 30 ms pulse (FIG. 8B) is evidenced at a frequency of 200 Hz.

Example 3 Administration of Ramped Waveform

This example presents data showing administration of high frequency AChaving a ramped waveform to skeletal muscle of adult swine.

In experiments in adult swine, an accepted surrogate of shock-inducedpain, the effect of high frequency AC on skeletal muscle stimulation wastested and compared with that observed during standard ICD shocks ascontrol. Application of high frequency AC (1 kHz) ramped in amplitudefrom 0 to 100 V over 1 sec (FIG. 9A) to the hind limb produced a gradualtetanic muscle contraction without significant further muscle responseto 400 V biphasic shock immediately following the high frequency AC ramp(FIG. 9B), whereas application of a 400 V standard biphasic shock aloneelicited a sudden sharp contraction of the limb (FIG. 9C), like thatseen during cardiac defibrillation. HFAC blunts the amplitude andespecially the rate of force developed in skeletal muscle, which resultsin substantial mitigation of defibrillation-induced pain.

Although the invention has been described with reference to the aboveexamples, it will be understood that modifications and variations areencompassed within the spirit and scope of the invention. Accordingly,the invention is limited only by the following claims.

What is claimed is:
 1. A device comprising: a housing configured to bepositioned external to the patient; and a waveform generator configuredto generate an alternating current (AC) and an electrical shock, thewaveform generator being disposed in the housing and the waveformgenerator is configured to be connected electrically to at least oneelectrode configured to be positioned externally on a patient; whereinthe electrical shock is at least 400 volts (V), and wherein the AC has afrequency in a range between 50 Hz to 20 kHz, has a duration, andincludes a ramped amplitude waveform defined by a gradually increasingpeak-to-peak amplitude of the AC during at least sixty percent of theduration.
 2. The device of claim 1, wherein the AC has a frequencybetween about 50 Hz to 310 Hz.
 3. The device of claim 1, wherein thedevice is configured to administer the AC after a delay from onset ofcardiac excitation.
 4. The device of claim 1, wherein the electricalshock is a biphasic electrical shock following application of the AC. 5.The device of claim 1, wherein the AC has a frequency between 50 Hz and500 Hz.
 6. The device of claim 1, wherein the AC has a frequency between500 Hz and 1 kHz.
 7. The device of claim 1, wherein the AC has afrequency between 250 Hz and 500 Hz.
 8. The device of claim 1, whereinthe electrical shock is delivered by the waveform generator immediatelyafter the end of the AC.
 9. The device of claim 1, wherein thepeak-to-peak amplitude of the AC increases until the application of theelectrical shock.
 10. The device of claim 1, wherein the peak-to-peakamplitude of the AC increases throughout the duration of the AC.
 11. Thedevice of claim 1, wherein the ramped amplitude waveform is a graduallyincreasing sine wave.
 12. The device of claim 1, wherein the rampedamplitude waveform is a gradually increasing triangular wave.
 13. Thedevice of claim 1, wherein the ramped amplitude waveform is a graduallyincreasing square wave.
 14. The device of claim 1, wherein theelectrical shock is administered after offset of the AC.
 15. The deviceof claim 1, wherein the electrical shock is administered after onset ofthe AC and no later than offset of the AC.
 16. The device of claim 1,wherein the duration in a range of 0.025 to 5 seconds.
 17. The device ofclaim 1, wherein the duration in a range of 0.025 to 2.0 seconds. 18.The device of claim 1, wherein the gradually increasing peak-to-peakamplitude increases for at least seventy percent of a duration of theAC.
 19. The device of claim 1, wherein the electrical shock is abiphasic electrical shock following application of the AC.
 20. A devicefor treating arrhythmia comprising: a waveform generator configured togenerate an alternating current (AC) and an electrical shock which areapplied to the at least one electrode configured to be appliedexternally to a torso of a patient; and a computer, logic circuit, ormicroprocessor configured to command the waveform generator to generateor deliver alternating current (AC) and the electrical shock to the atleast one electrode; wherein the waveform generator is configured togenerate the alternating current (AC) to have a frequency between 50 Hzand 20 kHz and a duration; wherein during at least sixty percent of theduration, the AC is defined by a ramped amplitude waveform having agradually increasing peak-to-peak amplitude of the AC, and wherein theelectrical shock is at least 400 volts (V).
 21. The device of claim 20,wherein the waveform generator is configured to generate an alternatingcurrent (AC) having a frequency between 50 Hz and 500 Hz.
 22. The deviceof claim 20, wherein the waveform generator is configured to generate analternating current (AC) having a frequency between 500 Hz and 1 kHz.23. The device of claim 20, wherein the waveform generator is configuredto generate an alternating current (AC) having a frequency between 250Hz and 500 Hz.
 24. The device of claim 20, wherein the device isconfigured to generate and administer a biphasic electrical shockfollowing application of AC.
 25. The device of claim 20, wherein thedevice is configured to generate and administer a biphasic electricalshock following application of AC.
 26. The device of claim 20, whereinthe electrical shock is administered after offset of the AC, or afteronset of the AC and before offset of the AC.
 27. The device of claim 20,wherein the duration is in a range of 0.025 to 5 seconds.
 28. The deviceof claim 20, wherein the duration is at least 0.050 seconds and theramped waveform rises for at least seventy percent of the duration. 29.The device of claim 20, wherein the duration is at least 0.100 secondsand the ramped waveform rises for at least eighty percent of theduration.
 30. The device of claim 20, wherein the frequency between 50Hz and 20 kHz is a plurality of frequencies between 50 Hz and 20 kHzgenerated during the duration.
 31. A device for treating arrhythmiacomprising: a housing configured to be positioned internal or externalto the patient; and a waveform generator configured to generate analternating current (AC) and an electrical shock which is applied to atleast one electrode configured to be applied to a patient, the waveformgenerator being disposed in the housing; wherein the electrical shock isat least 400 volts (V), and wherein the AC has a frequency in a rangebetween 50 Hz to 20 kHz, has a duration, and includes a ramped amplitudewaveform defined by a gradually increasing peak-to-peak amplitude of theAC during at least sixty percent of the duration.
 32. The device ofclaim 31, wherein the waveform generator is configured to generate AChaving a frequency between about 50 Hz to 500 Hz.
 33. The device ofclaim 31, wherein the electrodes are configured for intravascular orintracardiac positioning in the patient.
 34. The device of claim 31,wherein the electrodes are configured for extravascular or externalpositioning on the patient.
 35. The device of claim 31, wherein thedevice further comprises a sensing circuit for determining the presenceof arrhythmia.
 36. The device of claim 35, wherein the deviceautomatically generates the AC when arrhythmia is detected.
 37. Thedevice of claim 31, wherein the device is implantable.
 38. The device ofclaim 31, wherein the device further comprises a programmable logiccircuit, such that the device is configured to administer AC after adelay from onset of cardiac excitation.
 39. The device of claim 31,wherein the electrical shock is a biphasic electrical shock followingapplication of AC.
 40. The device of claim 31, wherein the waveformgenerator is configured to produce an alternating current (AC) having afrequency between 50 Hz and 500 Hz.
 41. The device of claim 31, whereinthe waveform generator is configured to produce alternating current (AC)having a frequency between 500 Hz and 1 kHz.
 42. The device of claim 31,wherein the waveform generator is configured to produce an alternatingcurrent (AC) having a frequency between 250 Hz and 500 Hz.
 43. Thedevice of claim 31, wherein the frequency between 50 Hz and 20 kHz is aplurality of frequencies between 50 Hz and 20 kHz generated during theduration.